Circuit breakers, in particular low-voltage circuit breakers, are electromagnetic automatic switches in the event of a short circuit. Their manner of operation corresponds, in principle, to the manner of operation of miniature circuit breakers. They are usually equipped with a thermal release and a magnetic release and therefore have the same design elements as miniature circuit breakers. However, they are designed for relatively high rated currents, and the releases of circuit breakers, in contrast to miniature circuit breakers, can furthermore be adjusted partially separately. The switches are also used as motor protection switches in the low-voltage range.
The task of the circuit breaker is to protect downstream installations and, in particular, three-phase motors against damage due to overloading or short-circuiting. In this case, the aim is for the circuit breaker to interrupt these currents in conjunction with the devices of the mains contactor. If gas is present between the two poles, it is ionized by the flashover when there is a correspondingly high voltage difference between the poles, and a self-maintained gas discharge, which is also called an arc, is formed. This plasma not only continues to conduct current but also reduces the service life of the component and may even destroy the switch given heavy currents. In contrast to disconnection devices, circuit breakers are designed such that the arc which is produced when the switching contacts are opened is quenched rapidly and without damaging the switch and, as a result, the current flow is interrupted.
Circuit breakers are developed in various installation sizes. In this case, an installation size is made up of device variants with a series of rated currents which expediently build on one another, wherein the power loss is approximately proportional to the square of the rated current. The device variant with the highest rated current at a given installation size is determined by, even for this current, the power loss conversion given a corresponding housing volume being maintained for the requirements of the switching device over its service life without disadvantageous consequences. If even higher rated currents are desired, a larger design is developed. However, from a customer's point of view, it is desirable to drive the maximum rated current within an installation size even higher. In order to achieve this, measures can be taken in order to make the dissipation of heat from the housing volume technically more efficient.
In principle, there are two options for dealing with high temperatures within a protective housing on account of unavoidable electrical power loss. From amongst said options, one option makes provision for all materials to be optimized to such an extent that they meet their functional requirements even at a high temperature level. However, this is a very costly solution.
The other option is to force the generated heat to be dissipated from the housing by technical measures. For electronic products, active cooling measures by way of housing fans, a heat pipe arrangement or even coolant circuits are known from the prior art. In order to be able to also dissipate large quantities of locally generated heat in this way, the quantities of heat are distributed over large areas by use of heat sinks.
Heat sinks of this kind are unsuitable for electromechanical switchgears. In this case, in addition to the connection lines, the heat is mainly dissipated via the freely accessible surfaces of the device, essentially the top side, feed side and device output side. In practice, this often leads to a high device temperature level and to disadvantageous, relatively concentrated heat pockets on account of the long heat path.